Hypoxia-sensitive micellar nanoparticles for co-delivery of siRNA and chemotherapeutics to overcome multi-drug resistance in tumor cells

Therapeutic delivery of siRNA for the management of breast cancer and triple-negative breast cancer

Breast cancer is the leading cause of cancer-related deaths among women globally. The difficulties with anticancer medications, such as ineffective targeting, larger doses, toxicity to healthy cells and side effects, have prompted attention to alternate approaches to address these difficulties. RNA interference by small interfering RNA (siRNA) is one such tactic. When compared with chemotherapy, siRNA has several advantages, including the ability to quickly modify and suppress the expression of the target gene and display superior efficacy and safety. However, there are known challenges and hurdles that limits their clinical translation. Decomposition by endonucleases, renal clearance, hydrophilicity, negative surface charge, short half-life and off-target effects of naked siRNA are obstacles that hinder the desired biological activity of naked siRNA. Nanoparticulate systems such as polymeric, lipid, lipid-polymeric, metallic, mesoporous silica nanoparticles and several other nanocarriers were used for effective delivery of siRNA and to knock down genes involved in breast cancer and triple-negative breast cancer. The focus of this review is to provide a comprehensive picture of various strategies utilized for delivering siRNA, such as combinatorial delivery, development of modified nanoparticles, smart nanocarriers and nanocarriers that target angiogenesis, cancer stem cells and metastasis of breast cancer.

Porous Organic Polymer-Based Nanocomposites for Hypoxia Relieving and Enhanced Chemotherapy in Hepatocellular Carcinoma

Uncontrolled proliferation and altered metabolism of cancer cells result in an imbalance of nutrients and oxygen supply, and persuade hypoxia. Hypoxia, in turn, activates the transcription gene HIF-1α, which eventually upregulates the efflux transporter P-gp and induces multidrug resistance (MDR). Thus, hypoxia leads to the development of resistance to conventional therapies. Therefore, the fabrication of a nanoscale porous system enriched with upconversion nanoparticles to target cancer cells, evade hypoxia, and enhance anticancer therapy is the key goal of this article. Herein, upconversion nanoparticles are embedded in a nanoscale porous organic polymer (POP) and further conjugated with a targeting moiety and a catalase molecule. The nanoscale POP embedded in UCNPs is generated at room temperature. The targeting ligand, lactobionic acid, is attached after polymer coating, which effectively targets liver cancer cells. Then, catalase is grafted effectively to produce oxygen. Endogenously generated oxygen alleviates hypoxia in liver cancer cells. The drug- and catalase-loaded composite exhibit greater cytotoxicity in hypoxic liver cells than in normal cells by overcoming hypoxia and downregulating the hypoxia-inducible factors.

Non-viral vectors combined delivery of siRNA and anti-cancer drugs to reverse tumor multidrug resistance

Multidrug resistance (MDR) of tumors is one of the main reasons for the failure of chemotherapy. Multidrug resistance refers to the cross-resistance of tumor cells to multiple antitumor drugs with different structures and mechanisms of action. Current strategies to reverse multidrug resistance in tumors include MDR inhibitors and RNAi technology. siRNA is a small molecule RNA that is widely used in RNAi technology and has the characteristics of being prepared in large quantities and chemically modified. However, siRNA is susceptible to degradation in vivo. The effect of siRNA therapy alone is not ideal, so siRNA and anticancer drugs are administered in combination to reverse the MDR of tumors. Non-viral vectors are now commonly used to deliver siRNA and anticancer drugs to tumor sites. This article will review the progress of siRNA and chemotherapeutic drug delivery systems and their mechanisms for reversing multidrug resistance.

Recent advanced lipid-based nanomedicines for overcoming cancer resistance

The increasing prevalence of cancer drug resistance not only critically limits the efficiency of traditional therapies but also causes relapses or recurrences of cancer. Consequently, there remains an urgent need to address the intricate landscape of drug resistance beyond traditional cancer therapies. Recently, nanotechnology has played an important role in the field of various drug delivery systems for the treatment of cancer, especially therapy-resistant cancer. Among advanced nanomedicine technologies, lipid-based nanomaterials have emerged as effective drug carriers for cancer treatment, significantly improving therapeutic effects. Due to their biocompatibility, simplicity of preparation, and potential for functionalization, lipid-based nanomaterials are considered powerful competitors for resistant cancer. In this review, an overview of lipid-based nanomaterials for addressing cancer resistance is discussed. We summarize the recent progress in overcoming drug resistance in cancer by these lipid-based nanomaterials, and highlight their potential in future applications to reverse cancer resistance.

Smart Nanoplatforms Responding to the Tumor Microenvironment for Precise Drug Delivery in Cancer Therapy

The tumor microenvironment (TME) is a complex and dynamic entity, comprising stromal cells, immune cells, blood vessels and extracellular matrix, which is intimately associated with the occurrence and development of cancers, as well as their therapy. Utilizing the shared characteristics of tumors, such as an acidic environment, enzymes and hypoxia, researchers have developed a promising cancer therapy strategy known as responsive release of nano-loaded drugs, specifically targeted at tumor tissues or cells. In this comprehensive review, we provide an in-depth overview of the current fundamentals and state-of-the-art intelligent strategies of TME-responsive nanoplatforms, which include acidic pH, high GSH levels, high-level adenosine triphosphate, overexpressed enzymes, hypoxia and reductive environment. Additionally, we showcase the latest advancements in TME-responsive nanoparticles. In conclusion, we thoroughly examine the immediate challenges and prospects of TME-responsive nanopharmaceuticals, with the expectation that the progress of these targeted nanoformulations will enable the exploitation, overcoming or modulation of the TME, ultimately leading to significantly more effective cancer therapy.

Strategies to overcome cancer multidrug resistance (MDR) through targeting P-glycoprotein (ABCB1): An updated review

The emergence of multidrug resistance (MDR) in malignant tumors is one of the leading threats encountered currently in many chemotherapeutic agents. The overexpression of the ATP-binding cassette (ABC) transporters is involved in MDR. P-glycoprotein (P-gp)/ABCB1 is a member of the ABC transporter family that significantly increases the efflux of various anticancer drugs from tumor cells. Therefore, targeting P-gp with small molecule inhibitors is an effective therapeutic strategy to overcome MDR. Over the past four decades, diverse compounds with P-gp inhibitory activity have been identified to sensitize drug-resistant cells, but none of them has been proven clinically useful to date. Research efforts continue to discover an effective approach for circumventing MDR. This review has provided an overview of the most recent advances (last three years) in various strategies for circumventing MDR mediated by P-gp. It may be helpful for the scientists working in the field of drug discovery to further synthesize and discover new chemical entities/therapeutic modalities with less toxicity and more efficacies to overcome MDR in cancer chemotherapy.

Phototriggered structures: Latest advances in biomedical applications

Non-invasive control of the drug molecules accessibility is a key issue in improving diagnostic and therapeutic procedures. Some studies have explored the spatiotemporal control by light as a peripheral stimulus. Phototriggered drug delivery systems (PTDDSs) have received interest in the past decade among biological researchers due to their capability the control drug release. To this end, a wide range of phototrigger molecular structures participated in the DDSs to serve additional efficiency and a high-conversion release of active fragments under light irradiation. Up to now, several categories of PTDDSs have been extended to upgrade the performance of controlled delivery of therapeutic agents based on well-known phototrigger molecular structures like o-nitrobenzyl, coumarinyl, anthracenyl, quinolinyl, o-hydroxycinnamate and hydroxyphenacyl, where either of one endows an exclusive feature and distinct mechanistic approach. This review conveys the design, photochemical properties and essential mechanism of the most important phototriggered structures for the release of single and dual (similar or different) active molecules that have the ability to quickly reason of the large variety of dynamic biological phenomena for biomedical applications like photo-regulated drug release, synergistic outcomes, real-time monitoring, and biocompatibility potential.

Nanocarriers overcoming biological barriers induced by multidrug resistance of chemotherapeutics in 2D and 3D cancer models

Multidrug resistance (MDR) is currently a big challenge in cancer therapy and limits its success in several patients. Tumors use the MDR mechanisms to colonize the host and reduce the efficacy of chemotherapeutics that are injected as single agents or combinations. MDR mechanisms are responsible for inactivation of drugs and formbiological barriers in cancer like the drug efflux pumps, aberrant extracellular matrix, hypoxic areas, altered cell death mechanisms, etc. Nanocarriers have some potential to overcome these barriers and improve the efficacy of chemotherapeutics. In fact, they are versatile and can deliver natural and synthetic biomolecules, as well as RNAi/DNAi, thus providing a controlled release of drugs and a synergistic effect in tumor tissues. Biocompatible and safe multifunctional biopolymers, with or without specific targeting molecules, modify the surface and interface properties of nanocarriers. These modifications affect the interaction of nanocarriers with cellular models as well as the selection of suitable models for in vitro experiments. MDR cancer cells, and particularly their 2D and 3D models, in combination with anatomical and physiological structures of tumor tissues, can boost the design and preparation of nanomedicines for anticancer therapy. 2D and 3D cancer cell cultures are suitable models to study the interaction, internalization, and efficacy of nanocarriers, the mechanisms of MDR in cancer cells and tissues, and they are used to tailor a personalized medicine and improve the efficacy of anticancer treatment in patients. The description of molecular mechanisms and physio-pathological pathways of these models further allow the design of nanomedicine that can efficiently overcome biological barriers involved in MDR and test the activity of nanocarriers in 2D and 3D models of MDR cancer cells.

Recent Advances in Nanoparticle-Mediated Co-Delivery System: A Promising Strategy in Medical and Agricultural Field

Drug and gene delivery systems mediated by nanoparticles have been widely studied for life science in the past decade. The application of nano-delivery systems can dramatically improve the stability and delivery efficiency of carried ingredients, overcoming the defects of administration routes in cancer therapy, and possibly maintaining the sustainability of agricultural systems. However, delivery of a drug or gene alone sometimes cannot achieve a satisfactory effect. The nanoparticle-mediated co-delivery system can load multiple drugs and genes simultaneously, and improve the effectiveness of each component, thus amplifying efficacy and exhibiting synergistic effects in cancer therapy and pest management. The co-delivery system has been widely reported in the medical field, and studies on its application in the agricultural field have recently begun to emerge. In this progress report, we summarize recent progress in the preparation and application of drug and gene co-delivery systems and discuss the remaining challenges and future perspectives in the design and fabrication.

Use of stimulatory responsive soft nanoparticles for intracellular drug delivery

Drug delivery has made tremendous advances in the last decade. Targeted therapies are increasingly common, with intracellular delivery highly impactful and sought after. Intracellular drug delivery systems have limitations due to imprecise and non-targeted release profiles. One way this can be addressed is through using stimuli-responsive soft nanoparticles, which contain materials with an organic backbone such as lipids and polymers. The choice of biomaterial is essential for soft nanoparticles to be responsive to internal or external stimuli. The nanoparticle must retain its integrity and payload in non-targeted physiological conditions while responding to particular intracellular environments where payload release is desired. Multiple internal and external factors could stimulate the intracellular release of drugs from nanoparticles. Internal stimuli include pH, oxidation, and enzymes, while external stimuli include ultrasound, light, electricity, and magnetic fields. Stimulatory responsive soft nanoparticulate systems specifically utilized to modulate intracellular delivery of drugs are explored in this review.

Nanoparticle-Based Combination Therapy for Ovarian Cancer

Ovarian cancer is one of the most common malignant tumors in gynecology with a high incidence. Combination therapy, eg, administration of paclitaxel followed by a platinum anticancer drug is recommended to treat ovarian cancer due to its advantages in, eg, reducing side effects and reversing (multi)drug-resistance compared to single treatment. However, the benefits of combination therapy are often compromised. In chemo and chemo/gene combinations, co-deposition of the combined therapeutics in the tumor cells is required, which is difficult to achieve due to dramatic pharmacokinetic differences between combinational agents in free forms. Moreover, some undesired properties such as the low-water solubility of chemodrugs and the difficulty of cellular internalization of gene therapeutics also hinder the therapeutic potential. Delivery of dual or multiple agents by nanoparticles provides opportunities to tackle these limits. Nanoparticles encapsulate hydrophobic drug(s) to yield aqueous dispersions facilitating its administration and/or to accommodate hydrophilic genes facilitating its access to cells. Moreover, nanoparticle-based therapeutics can not only improve drug properties (eg, in vivo stability) and ensure the same drug disposition behavior with controlled drug ratios but also can minimize drug exposure of the normal tissues and increase drug co-accumulation at targeted tissues via passive and/or active targeting strategies. Herein, this work summarizes nanoparticle-based combination therapies, mainly including anticancer drug-based combinations and chemo/gene combinations, and emphasizes the advantageous outcomes of nanocarriers in the combination treatment of ovarian cancer. In addition, we also review mechanisms of synergetic effects resulting from different combinations.

Polymeric micelles and cancer therapy: an ingenious multimodal tumor-targeted drug delivery system

Since the beginning of pharmaceutical research, drug delivery methods have been an integral part of it. Polymeric micelles (PMs) have emerged as multifunctional nanoparticles in the current technological era of nanocarriers, and they have shown promise in a range of scientific fields. They can alter the release profile of integrated pharmacological substances and concentrate them in the target zone due to their improved permeability and retention, making them more suitable for poorly soluble medicines. With their ability to deliver poorly soluble chemotherapeutic drugs, PMs have garnered considerable interest in cancer. As a result of their remarkable biocompatibility, improved permeability, and minimal toxicity to healthy cells, while also their capacity to solubilize a wide range of drugs in their micellar core, PMs are expected to be a successful treatment option for cancer therapy in the future. Their nano-size enables them to accumulate in the tumor microenvironment (TME) via the enhanced permeability and retention (EPR) effect. In this review, our major aim is to focus primarily on the stellar applications of PMs in the field of cancer therapeutics along with its mechanism of action and its latest advancements in drug and gene delivery (DNA/siRNA) for cancer, using various therapeutic strategies such as crossing blood-brain barrier, gene therapy, photothermal therapy (PTT), and immunotherapy. Furthermore, PMs can be employed as "smart drug carriers," allowing them to target specific cancer sites using a variety of stimuli (endogenous and exogenous), which improve the specificity and efficacy of micelle-based targeted drug delivery. All the many types of stimulants, as well as how the complex of PM and various anticancer drugs react to it, and their pharmacodynamics are also reviewed here. In conclusion, commercializing engineered micelle nanoparticles (MNPs) for application in therapy and imaging can be considered as a potential approach to improve the therapeutic index of anticancer drugs. Furthermore, PM has stimulated intense interest in research and clinical practice, and in light of this, we have also highlighted a few PMs that have previously been approved for therapeutic use, while the majority are still being studied in clinical trials for various cancer therapies.

Co-delivery of carbonic anhydrase IX inhibitor and doxorubicin as a promising approach to address hypoxia-induced chemoresistance

Hypoxia, an oxygen-deprived condition of the tumor, is one of the major reasons for resistance to chemotherapy. Carbonic anhydrases are generally involved in pH homeostasis in normal conditions, but in solid tumors having a strong relation with hypoxia, the carbonic anhydrase IX (CA-IX) enzyme is overexpressed and results in an extracellular acidic environment. For most weakly basic anticancer drugs, including doxorubicin (Dox), the ionization in an acidic environment limits their cellular uptake, and consequently, the tumor exposure to the drug at sub-therapeutic concentration comes out as chemoresistance. Herein, a combined drug delivery system of liposomes and mesoporous silica nanoparticles (MSNPs) was developed for the co-delivery of the CA-IX enzyme inhibitor and Dox in hypoxic condition. The unique structure of MSNPs with higher surface area was utilized for higher drug loading and sustained release of Dox. Additionally, the biocompatible nature of liposomal coating as a second loading site for the CA-IX enzyme inhibitor has provided gatekeeping effects at pore opening to avoid premature drug release. Lipid coated MSNPs as a co-delivery system for Dox and the CA-IX inhibitor have synergistic cytotoxic effects against MDA-MB 231 breast cancer cells in hypoxic conditions. These findings assure the potential of this drug delivery system to overcome hypoxia-related chemoresistance.

Broadening the Horizons of RNA Delivery Strategies in Cancer Therapy

RNA-based therapy is a promising and innovative strategy for cancer treatment. However, poor stability, immunogenicity, low cellular uptake rate, and difficulty in endosomal escape are considered the major obstacles in the cancer therapy process, severely limiting the development of clinical translation and application. For efficient and safe transport of RNA into cancer cells, it usually needs to be packaged in appropriate carriers so that it can be taken up by the target cells and then be released to the specific location to perform its function. In this review, we will focus on up-to-date insights of the RNA-based delivery carrier and comprehensively describe its application in cancer therapy. We briefly discuss delivery obstacles in RNA-mediated cancer therapy and summarize the advantages and disadvantages of different carriers (cationic polymers, inorganic nanoparticles, lipids, etc.). In addition, we further summarize and discuss the current RNA therapeutic strategies approved for clinical use. A comprehensive overview of various carriers and emerging delivery strategies for RNA delivery, as well as the current status of clinical applications and practice of RNA medicines are classified and integrated to inspire fresh ideas and breakthroughs.

Emerging nanotechnology-based therapeutics to combat multidrug-resistant cancer

Cancer often develops multidrug resistance (MDR) when cancer cells become resistant to numerous structurally and functionally different chemotherapeutic agents. MDR is considered one of the principal reasons for the failure of many forms of clinical chemotherapy. Several factors are involved in the development of MDR including increased expression of efflux transporters, the tumor microenvironment, changes in molecular targets and the activity of cancer stem cells. Recently, researchers have designed and developed a number of small molecule inhibitors and derivatives of natural compounds to overcome various mechanisms of clinical MDR. Unfortunately, most of the chemosensitizing approaches have failed in clinical trials due to non-specific interactions and adverse side effects at pharmacologically effective concentrations. Nanomedicine approaches provide an efficient drug delivery platform to overcome the limitations of conventional chemotherapy and improve therapeutic effectiveness. Multifunctional nanomaterials have been found to facilitate drug delivery by improving bioavailability and pharmacokinetics, enhancing the therapeutic efficacy of chemotherapeutic drugs to overcome MDR. In this review article, we discuss the major factors contributing to MDR and the limitations of existing chemotherapy- and nanocarrier-based drug delivery systems to overcome clinical MDR mechanisms. We critically review recent nanotechnology-based approaches to combat tumor heterogeneity, drug efflux mechanisms, DNA repair and apoptotic machineries to overcome clinical MDR. Recent successful therapies of this nature include liposomal nanoformulations, cRGDY-PEG-Cy5.5-Carbon dots and Cds/ZnS core–shell quantum dots that have been employed for the effective treatment of various cancer sub-types including small cell lung, head and neck and breast cancers.

Polymeric nanoparticles-siRNA as an emerging nano-polyplexes against ovarian cancer

Ovarian cancer (OC) is considered fifth-deadliest cancer globally responsible for high mortality in women. As the conventional therapeutic and diagnostic approaches are ineffective in increasing the survival rates of advanced staged patients by more than 5 years, OC has resulted in high morbidity and mortality rates over the last two decades. As a result, there is a dire need for innovative treatment approaches to address the issues. RNAi and nanotechnology can be considered the most appropriate strategies that can be used to improve OC therapy and help circumvent the chemo-resistance. siRNA is considered highly successful in facilitating the knockdown of specific genes on entering the cytosol when administered in-vivo via inhibiting the mRNA expression responsible for translation of those specific genes through the mechanism called RNA interference (RNAi). However, the primary barrier of utmost importance in the clinical efficacy of employed siRNA for the treatment of OC is the systemic distribution to the targeted site from the administration site. As a result, nanoparticles are constructed to carry the siRNA molecules inside them to the targeted site by preventing serum degradation and enhancing the serum stability of administered siRNA. The present review assesses the developments made in the polymeric-based nanoparticle siRNA delivery for targeting particular genes involved in the prognosis of ovarian cancers and surpassing the chemo-resistance and thus improving the therapeutic potentials of administered agents.

Recent Advances in Nanoparticle-Based Co-Delivery Systems for Cancer Therapy

Cancer therapies have advanced tremendously throughout the last decade, yet multiple factors still hinder the success of the different cancer therapeutics. The traditional therapeutic approach has been proven insufficient and lacking in the suppression of tumor growth. The simultaneous delivery of multiple small-molecule chemotherapeutic drugs and genes improves the effectiveness of each treatment, thus optimizing efficacy and improving synergistic effects. Nanomedicines integrating inorganic, lipid, and polymeric-based nanoparticles have been designed to regulate the spatiotemporal release of the encapsulated drugs. Multidrug-loaded nanocarriers are a potential strategy to fight cancer and the incorporation of co-delivery systems as a feasible treatment method has projected synergistic benefits and limited undesirable effects. Moreover, the development of co-delivery systems for maximum therapeutic impact necessitates better knowledge of the appropriate therapeutic agent ratio as well as the inherent heterogeneity of the cancer cells. Co-delivery systems can simplify clinical processes and increase patient quality of life, even though such systems are more difficult to prepare than single drug delivery systems. This review highlights the progress attained in the development and design of nano carrier-based co-delivery systems and discusses the limitations, challenges, and future perspectives in the design and fabrication of co-delivery systems.

A novel and easy to prepare azo-based bioreductive linker and its application in hypoxia-sensitive cationic liposomal doxorubicin: Synthesis, characterization, in vitro and in vivo studies in mice bearing C26 tumor

This study designed and synthesized a cost-effective azo-based hypoxia-sensitive linker (AHSL) using commercially accessible, inexpensive raw materials and simple methods to apply in cationic nanoliposomes. Then, AHSL was post-inserted into the cationic liposome (Cat-lip), and PEG-Azo-Cat-lip was prepared and characterized using DLS. The decrease in the zeta-potential of formulation from + 18.4 mV for Cat-lip to + 6.1 mV and the increase in the size of the PEG-Azo-Cat-lip indicated the successful post insertion of AHSL into the liposomes. The Doxorubicin (Dox) release study showed that PEGylation results in a more stable PEG-Azo-Cat-lip than the Cat-lip. The increased cytotoxicity of the PEG-Azo-Cat-lip in the hypoxic condition also indicated the cleavage of the AHSL in the hypoxic environment. In vivo biodistribution using animal imaging has shown higher tumor accumulation of the MPEG-Azo-Cat-lip than Cat-lip during the 120 h of the study. The results of anti-tumor activities and biosafety of the formulations also showed the higher efficiency of the MPEG-Azo-Cat-lip compared with the Cat-lip. The results of this study indicated the antitumor efficacy of this hypoxia-sensitive which merits further investigation.

Preparation of 2-Methoxyestradiol Self-emulsified Drug Delivery System and the Effect on Combination Therapy with Doxorubicin Against MCF-7/ADM Cells

Due to the poor solubility and bioavailability of 2-methoxyestradiol (2-ME), 2-ME emulsified drug delivery system (2-ME-SEDDS) was designed and characterized. After dilution with 5% glucose, 2-ME-SEDDS formed fine emulsions with mean diameter of 171 ± 14 nm and zeta potential of - 7.4 ± 0.6 mV. The cytotoxicity of 2-ME-SEDDS against MCF-7 and MCF-7/ADM cells was considerable to that of free 2-ME, and the half maximal inhibitory concentration ran up to 195 µg/mL on MCF-7/ADM cells. In order to gain a satisfactory inhibition effect on MCF-7/ADM cells, 2-ME-SEDDS combined with doxorubicin was used. It is worth noting that the combination of 2-ME-SEDDS and doxorubicin displayed a superior synergistic effect with a combined index of 0.62. And the cellular uptake of doxorubicin by MCF-7/ADM cells in the combination group was significantly higher than that of doxorubicin treatment group. The study preliminarily suggested that 2-ME-SEDDS could increase the cellular uptake of doxorubicin by MCF-7/ADM cells and the synergistic effect may be attributed to the increased cellular uptake of doxorubicin under the influence of 2-ME-SEDDS. In conclusion, SEDDS was an alternative and promising formulation for 2-ME. The combination therapy with synergistic effect by the combination of 2-ME-SEDDS and doxorubicin seems to be a promising strategy to potentiate anti-tumor efficiency against MCF-7/ADM, even other multidrug resistance tumors.

Exosome-based nanomedicine for cancer treatment by targeting inflammatory pathways: Current status and future perspectives

Cancer is one of the dreadful diseases worldwide. Surgery, radiation and chemotherapy, are the three basic standard modes of cancer treatment. However, difficulties in cancer treatment are increasing due to immune escape, spreading of cancer to other places, and resistance of cancer cells to therapies. Various signaling mechanisms, including PI3K/Akt/mTOR, RAS, WNT/β-catenin, TGF-beta, and notch pathways, are involved in cancer resistance. The adaptive inflammatory response is the initial line of defence against infection. However, chronic inflammation can lead to tumorigenesis, malignant transformation, tumor growth, invasion, and metastasis. The most commonly dysregulated inflammatory pathways linked to cancer include NF-κB, MAPK, JAK-STAT, and PI3K/AKT. To overcome major hurdles in cancer therapy, nanomedicine is receiving much attention due to its role as a vehicle for delivering chemotherapeutic agents that specifically target tumor sites. Several biocompatible nanocarriers including polymer and inorganic nanoparticles, liposomes, micellar nanoparticles, nanotubes, and exosomes have been extensively studied. Exosome has been reported as an important potential sytem that could be effectively used as a bioinspired, bioengineered, and biomimetic drug delivery solution considering its toxicity, immunogenicity, and rapid clearance by the mononuclear phagocyte system. Exosome-mimetic vesicles are receiving much interest for developing nano-sized delivery systems. In this review, exosomes in detail as well as certain other nanocarriers, and their potential therapeutic roles in cancer therapy has been thoroughly discussed. Additionally, we also reviewed on oncogenic and tumor suppressor proteins, inflammation, and their associated signaling pathways and their interference by exosomes based nanomedicine.

Polyethyleneimine (PEI) as a Polymer-Based Co-Delivery System for Breast Cancer Therapy

Cancer has become one of the leading causes of morbidity and mortality worldwide. This disease is classified broadly by tissue, organ, and system; different cancer types and subtypes require different treatments. Drug bioavailability, selectivity, and high dosage, as well as extended treatment, are significantly associated with the development of resistance – a complex problem in cancer therapy. It is expected that the combination of anticancer drugs and drug delivery systems, using polymers to increase the access of such agents to their site of action, will improve the efficacy of therapy. Polyethyleneimine (PEI) is a polymer used as a co-delivery system for anticancer drugs and gene therapy. PEI is also useful for other purposes, such as transfection and bio-adsorbent agents. In co-delivery, PEI can promote drug internalization. However, PEI with a high molecular weight is linked to higher cytotoxicity, thus requiring further evaluation of clinical safety. This review focuses on the utilization of PEI as a co-delivery system for anticancer therapy, as well as its potential to overcome resistance, particularly in the treatment of specific subtypes (eg, breast cancer). In conclusion, PEI has promising applications and is improvable for the development of anticancer drugs.

Triggered azobenzene-based prodrugs and drug delivery systems

Azobenzene-based molecules show unique trans-cis isomerization upon ultraviolet light irradiation, which induce the change of polarity, crystallinity, stability, and binding affinity with pharmacological target. Moreover, azobenzene is the substrate of azoreductase that is often overexpressed in many pathological sites, e.g. hypoxic solid tumor. Therefore, azobenzene can be a multifunctional molecule in material science, pharmaceutical science and biomedicine because of its sensitivity to light, hypoxia and certain enzymes, hence showing potential application in site-specific smart therapy. Herein we focus on the employment of azobenzene and its derivatives for engineering triggered prodrug and drug delivery systems, and provide an overview of photoswitchable azo-based prodrugs, the associated problems regarding ultraviolet light and reversible isomerization, as well as the potential solutions. We also present the advance of azo-bearing delivery vehicles wherein azobenzene act as the linker, capping agent, and building block, and discuss the corresponding mechanisms for controlled cargo release, endocytosis enhancement and sensitization of free radical cancer therapy.

Doxorubicin-loaded graphene oxide nanocomposites in cancer medicine: Stimuli-responsive carriers, co-delivery and suppressing resistance

INTRODUCTION

The application of doxorubicin (DOX) in cancer therapy has been limited due to its drug resistance and poor internalization. Graphene oxide (GO) nanostructures have the capacity for DOX delivery while promoting its cytotoxicity in cancer.

AREAS COVERED

The favorable characteristics of GO nanocomposites, preparation method, and application in cancer therapy are described. Then, DOX resistance in cancer is discussed. The GO-mediated photothermal therapy and DOX delivery for cancer suppression are described. Preparation of stimuli-responsive GO nanocomposites, surface functionalization, hybrid nanoparticles, and theranostic applications are emphasized in DOX chemotherapy.

EXPERT OPINION

Graphene oxide nanoparticle-based photothermal therapy maximizes the anti-cancer activity of DOX against cancer cells. Apart from DOX delivery, GO nanomaterials are capable of loading anti-cancer agents and genetic tools to minimize drug resistance and enhance the cytolytic impact of DOX in cancer eradication. To enhance DOX accumulation in cancer cells, stimuli-responsive (redox-, light-, enzyme- and pH-sensitive) GO nanoparticles have been developed for DOX delivery. Further development of targeted delivery of DOX-loaded GO nanomaterials against cancer cells may be achieved by surface modification of polymers such as polyethylene glycol, hyaluronic acid, and chitosan. Doxorubicin-loaded GO nanoparticles have demonstrated theranostic potential for simultaneous diagnosis and therapy. Hybridization of GO with other nanocarriers such as silica and gold nanoparticles further broadens their potential anti-cancer therapy applications.

Emerging Nano-Based Strategies Against Drug Resistance in Tumor Chemotherapy

Drug resistance is the most significant causes of cancer chemotherapy failure. Various mechanisms of drug resistance include tumor heterogeneity, tumor microenvironment, changes at cellular levels, genetic factors, and other mechanisms. In recent years, more attention has been paid to tumor resistance mechanisms and countermeasures. Nanomedicine is an emerging treatment platform, focusing on alternative drug delivery and improved therapeutic effectiveness while reducing side effects on normal tissues. Here, we reviewed the principal forms of drug resistance and the new possibilities that nanomaterials offer for overcoming these therapeutic barriers. Novel nanomaterials based on tumor types are an excellent modality to equalize drug resistance that enables gain more rational and flexible drug selectivity for individual patient treatment. With the emergence of advanced designs and alternative drug delivery strategies with different nanomaterials, overcome of multidrug resistance shows promising and opens new horizons for cancer therapy. This review discussed different mechanisms of drug resistance and recent advances in nanotechnology-based therapeutic strategies to improve the sensitivity and effectiveness of chemotherapeutic drugs, aiming to show the advantages of nanomaterials in overcoming of drug resistance for tumor chemotherapy, which could accelerate the development of personalized medicine.

Hypoxia-sensitive drug delivery to tumors

Achievement of a high dose of drug in the tumor while minimizing its systemic side effects is one of the important features of an improved drug delivery system. Thus, developing responsive carriers for site-specific delivery of chemotherapeutic agents has become a main goal of research efforts. One of the known hallmarks of cancerous tumors is hypoxia, which offers a target for selective drug delivery. The stimuli-sensitive micellar system developed by us, (PEG-azobenzene-PEI-DOPE (PAPD) has proven to be effective in vitro. The proposed construct developed, PAPD, contains an azobenzene group as a hypoxia-sensitive moiety that triggers the shedding of the PEG layer from the nanoparticle surface under conditions of hypoxia to improve cellular uptake. Using microfluidics, we show significantly improved cellular association and penetration under hypoxia in both single cells and in a 3D tumor model. Employing an in vivo model, we demonstrate slower tumor growth that did not induce systemic side effects, including weight loss in an experimental animal model, when compared to the free drug treatment. This complex-in-nature but simple-in-design system for the simultaneous delivery of siRNA to silence the P-glycoprotein and doxorubicin with active tumor targeting and proven therapeutic efficacy represents a universal platform for the delivery of other hydrophobic chemotherapeutic agents and siRNA molecules which can be further modified.

Hyaluronic acid-based nanoplatforms for Doxorubicin: A review of stimuli-responsive carriers, co-delivery and resistance suppression

An important motivation for the use of nanomaterials and nanoarchitectures in cancer therapy emanates from the widespread emergence of drug resistance. Although doxorubicin (DOX) induces cell cycle arrest and DNA damage by suppressing topoisomerase activity, resistance to DOX has severely restricted its anti-cancer potential. Hyaluronic acid (HA) has been extensively utilized for synthesizing nanoparticles as it interacts with CD44 expressed on the surface of cancer cells. Cancer cells can take up HA-modified nanoparticles through receptor-mediated endocytosis. Various types of nanostructures such as carbon nanomaterials, lipid nanoparticles and polymeric nanocarriers have been modified with HA to enhance the delivery of DOX to cancer cells. Hyaluronic acid-based advanced materials provide a platform for the co-delivery of genes and drugs along with DOX to enhance the efficacy of anti-cancer therapy and overcome chemoresistance. In the present review, the potential methods and application of HA-modified nanostructures for DOX delivery in anti-cancer therapy are discussed.

Nanotherapeutics approaches to overcome P-glycoprotein-mediated multi-drug resistance in cancer

Multidrug resistance (MDR) in cancer chemotherapy is a growing concern for medical practitioners. P-glycoprotein (P-gp) overexpression is one of the major reasons for multidrug resistance in cancer chemotherapy. The P-gp overexpression in cancer cells depends on several factors like adenosine triphosphate (ATP) hydrolysis, hypoxia-inducible factor 1 alpha (HIF-1α), and drug physicochemical properties such as lipophilicity, molecular weight, and molecular size. Further multiple exposures of anticancer drugs to the P-gp efflux protein cause acquired P-gp overexpression. Unique structural and functional characteristics of nanotechnology-based drug delivery systems provide opportunities to circumvent P-gp mediated MDR. The primary mechanism behind the nanocarrier systems in P-gp inhibition includes: bypassing or inhibiting the P-gp efflux pump to combat MDR. In this review, we discuss the role of P-gp in MDR and highlight the recent progress in different nanocarriers to overcome P-gp mediated MDR in terms of their limitations and potentials.

Advances in Nanomaterials Used in Co-Delivery of siRNA and Small Molecule Drugs for Cancer Treatment

Recent advancements in nanotechnology have improved our understanding of cancer treatment and allowed the opportunity to develop novel delivery systems for cancer therapy. The biological complexities of cancer and tumour micro-environments have been shown to be highly challenging when treated with a single therapeutic approach. Current co-delivery systems which involve delivering small molecule drugs and short-interfering RNA (siRNA) have demonstrated the potential of effective suppression of tumour growth. It is worth noting that a considerable number of studies have demonstrated the synergistic effect of co-delivery systems combining siRNA and small molecule drugs, with promising results when compared to single-drug approaches. This review focuses on the recent advances in co-delivery of siRNA and small molecule drugs. The co-delivery systems are categorized based on the material classes of drug carriers. We discuss the critical properties of materials that enable co-delivery of two distinct anti-tumour agents with different properties. Key examples of co-delivery of drug/siRNA from the recent literature are highlighted and discussed. We summarize the current and emerging issues in this rapidly changing field of research in biomaterials for cancer treatments.

Exploring new Horizons in overcoming P-glycoprotein-mediated multidrug-resistant breast cancer via nanoscale drug delivery platforms

The high probability (13%) of women developing breast cancer in their lifetimes in America is exacerbated by the emergence of multidrug resistance after exposure to first-line chemotherapeutic agents. Permeation glycoprotein (P-gp)-mediated drug efflux is widely recognized as the major driver of this resistance. Initial in vitro and in vivo investigations of the co-delivery of chemotherapeutic agents and P-gp inhibitors have yielded satisfactory results; however, these results have not translated to clinical settings. The systemic delivery of multiple agents causes adverse effects and drug-drug interactions, and diminishes patient compliance. Nanocarrier-based site-specific delivery has recently gained substantial attention among researchers for its promise in circumventing the pitfalls associated with conventional therapy. In this review article, we focus on nanocarrier-based co-delivery approaches encompassing a wide range of P-gp inhibitors along with chemotherapeutic agents. We discuss the contributions of active targeting and stimuli responsive systems in imparting site-specific cytotoxicity and reducing both the dose and adverse effects.

A folate-targeted PEGylated cyclodextrin-based nanoformulation achieves co-delivery of docetaxel and siRNA for colorectal cancer

Docetaxel (DTX) is a chemotherapeutic agent used for a range of cancers, but it has little activity against colorectal cancer (CRC). However, combination therapy with other therapeutic agents is a potential strategy to enhance the efficacy of DTX in CRC treatment. The nuclear factor-κB (NF-κB) signaling pathway is implicated in a variety of malignancies (e.g., CRC), and the blockade of NF-κB may increase the sensitivity of cancer cells to chemotherapy. The application of small interference RNA (siRNA) to inhibit the translation of complementary mRNA has demonstrated the potential for cancer gene therapy. In this study, an amphiphilic cationic cyclodextrin (CD) nanoparticle modified with PEGylated folate (FA; a ligand to target folate receptor on CRC) has been developed for co-delivery of DTX and siRNA (against the RelA, a subunit of NF-κB) in the treatment of CRC. The resultant co-formulation (CD.DTX.siRelA.PEG-FA) achieved cell-specific uptake indicating the function of the folate targeting ligand. The CD.DTX.siRelA.PEG-FA nanoparticle enhanced the apoptotic effect of DTX with the downregulation of RelA expression, which significantly retarded the growth of CRC in mice, without causing significant toxicity. These results suggest that the FA-targeted PEGylated CD-based co-formulation provides a promising strategy for combining DTX and siRNA in treating CRC.

Recent Advances in Tumor Targeting via EPR Effect for Cancer Treatment

Cancer causes the second-highest rate of death world-wide. A major shortcoming inherent in most of anticancer drugs is their lack of tumor selectivity. Nanodrugs for cancer therapy administered intravenously escape renal clearance, are unable to penetrate through tight endothelial junctions of normal blood vessels and remain at a high level in plasma. Over time, the concentration of nanodrugs builds up in tumors due to the EPR effect, reaching several times higher than that of plasma due to the lack of lymphatic drainage. This review will address in detail the progress and prospects of tumor-targeting via EPR effect for cancer therapy.

Cell membrane cloaked nanomedicines for bio-imaging and immunotherapy of cancer: Improved pharmacokinetics, cell internalization and anticancer efficacy

Despite enormous advancements in the field of oncology, the innocuous and effectual treatment of various types of malignancies remained a colossal challenge. The conventional modalities such as chemotherapy, radiotherapy, and surgery have been remained the most viable options for cancer treatment, but lacking of target-specificity, optimum safety and efficacy, and pharmacokinetic disparities are their impliable shortcomings. Though, in recent decades, numerous encroachments in the field of onco-targeted drug delivery have been adapted but several limitations (i.e., short plasma half-life, early clearance by reticuloendothelial system, immunogenicity, inadequate internalization and localization into the onco-tissues, chemoresistance, and deficient therapeutic efficacy) associated with these onco-targeted delivery systems limits their clinical viability. To abolish the aforementioned inadequacies, a promising approach has been emerged in which stealthing of synthetic nanocarriers has been attained by cloaking them into the natural cell membranes. These biomimetic nanomedicines not only retain characteristics features of the synthetic nanocarriers but also inherit the cell-membrane intrinsic functionalities. In this review, we have summarized preparation methods, mechanism of cloaking, and pharmaceutical and therapeutic superiority of cell-membrane camouflaged nanomedicines in improving the bio-imaging and immunotherapy against various types of malignancies. These pliable adaptations have revolutionized the current drug delivery strategies by optimizing the plasma circulation time, improving the permeation into the cancerous microenvironment, escaping the immune evasion and rapid clearance from the systemic circulation, minimizing the immunogenicity, and enabling the cell-cell communication via cell membrane markers of biomimetic nanomedicines. Moreover, the preeminence of cell-membrane cloaked nanomedicines in improving the bio-imaging and theranostic applications, alone or in combination with phototherapy or radiotherapy, have also been pondered.

Nanoparticles as Drug Delivery Systems of RNAi in Cancer Therapy

RNA interference (RNAi) can mediate gene-silencing by knocking down the expression of a target gene via cellular machinery with much higher efficiency in contrast to other antisense-based approaches which represents an emerging therapeutic strategy for combating cancer. Distinct characters of nanoparticles, such as distinctive size, are fundamental for the efficient delivery of RNAi therapeutics, allowing for higher targeting and safety. In this review, we present the mechanism of RNAi and briefly describe the hurdles and concerns of RNAi as a cancer treatment approach in systemic delivery. Furthermore, the current nanovectors for effective tumor delivery of RNAi therapeutics are classified, and the characteristics of different nanocarriers are summarized.

Harnessing amphiphilic polymeric micelles for diagnostic and therapeutic applications: Breakthroughs and bottlenecks

Amphiphilic block copolymers are widely utilized in the design of formulations owing to their unique physicochemical properties, flexible structures and functional chemistry. Amphiphilic polymeric micelles (APMs) formed from such copolymers have gained attention of the drug delivery scientists in past few decades for enhancing the bioavailability of lipophilic drugs, molecular targeting, sustained release, stimuli-responsive properties, enhanced therapeutic efficacy and reducing drug associated toxicity. Their properties including ease of surface modification, high surface area, small size, and enhanced permeation as well as retention (EPR) effect are mainly responsible for their utilization in the diagnosis and therapy of various diseases. However, some of the challenges associated with their use are premature drug release, low drug loading capacity, scale-up issues and their poor stability that need to be addressed for their wider clinical utility and commercialization. This review describes comprehensively their physicochemical properties, various methods of preparation, limitations followed by approaches employed for the development of optimized APMs, the impact of each preparation technique on the physicochemical properties of the resulting APMs as well as various biomedical applications of APMs. Based on the current scenario of their use in treatment and diagnosis of diseases, the directions in which future studies need to be carried out to explore their full potential are also discussed.

Employing siRNA tool and its delivery platforms in suppressing cisplatin resistance: Approaching to a new era of cancer chemotherapy

Although chemotherapy is a first option in treatment of cancer patients, drug resistance has led to its failure, requiring strategies to overcome it. Cancer cells are capable of switching among molecular pathways to ensure their proliferation and metastasis, leading to their resistance to chemotherapy. The molecular pathways and mechanisms that are responsible for cancer progression and growth, can be negatively affected for providing chemosensitivity. Small interfering RNA (siRNA) is a powerful tool extensively applied in cancer therapy in both pre-clinical (in vitro and in vivo) and clinical studies because of its potential in suppressing tumor-promoting factors. As such oncogene pathways account for cisplatin (CP) resistance, their targeting by siRNA plays an important role in reversing chemoresistance. In the present review, application of siRNA for suppressing CP resistance is discussed. The first priority of using siRNA is sensitizing cancer cells to CP-mediated apoptosis via down-regulating survivin, ATG7, Bcl-2, Bcl-xl, and XIAP. The cancer stem cell properties and related molecular pathways including ID1, Oct-4 and nanog are inhibited by siRNA in CP sensitivity. Cell cycle arrest and enhanced accumulation of CP in cancer cells can be obtained using siRNA. In overcoming siRNA challenges such as off-targeting feature and degradation, carriers including nanoparticles and biological carriers have been applied. These carriers are important in enhancing cellular accumulation of siRNA, elevating gene silencing efficacy and reversing CP resistance.

Electron-Accepting Micelles Deplete Reduced Nicotinamide Adenine Dinucleotide Phosphate and Impair Two Antioxidant Cascades for Ferroptosis-Induced Tumor Eradication

Ferroptotic antitumor therapy has been compromised by various intracellular antioxidants, particularly glutathione and thioredoxin. Both are cofactors of glutathione peroxide 4 (GPX4) that act against oxidative stress via catalyzing the reduction of lipid peroxides. It was postulated that tailored polymer micelles could enhance ferroptotic antitumor efficacy via diminishing glutathione and thioredoxin under hypoxia. The aim was to engineer hypoxia-responsive micelles for selective enhancement of ferroptotic cell death in solid tumor. The polymer contains hydrophilic poly(ethylene glycol) (PEG) that is linked by azobenzene linker with nitroimidazole-conjugated polypeptide. The tailored polymer could self-assemble into nanoscale micelles to encapsulate RAS-selective lethal small molecule 3, a covalent GPX4 inhibitor. Under hypoxia, the azobenzene moiety enabled PEG shedding and enhanced micelles uptake in 4T1 cells. Likewise, the nitroimidazole moiety was reduced by the overexpressed nitroreductase with reduced nicotinamide adenine dinucleotide phosphate (NADPH) as the cofactor, resulting in transient depletion of NADPH. This impaired both the glutathione and thioredoxin redox cycle, leading to diminished intracellular glutathione and thioredoxin. The selective potency of ferroptotic micelles in depleting NADPH, glutathione and thioredoxin was further verified in vivo in the 4T1 tumor xenograft mice model. This work highlights the role of hypoxia-responsive polymers in enhancing the potency of ferroptotic inducers against solid tumors without additional side effects to healthy organs.